Land management effects on wet aggregate stability and carbon content. Issue 6 (8th October 2021)

• Record Type: Journal Article
• Authors: Mikha, Maysoon M.; Jin, Virginia L.; Johnson, Jane M. F.; Lehman, R. Michael; Karlen, Douglas L.; Jabro, Jalal D.
• Is Part Of: Soil Science Society of America Journal. Volume 85:Issue 6(2021)
• Page Start: 2149
• Page End: 2168
• Publication Date: 2021-10-08
• Subjects: Soils -- United States -- Periodicals; Soil science -- Periodicals; Periodicals; 631.4973
• DOI: 10.1002/saj2.20333
• Languages: English
• ISSNs: 0361-5995

Abstract

Abstract: Land management affects soil structure and many other soil properties and processes. Our objectives were to evaluate soil organic C (SOC), aggregate size distribution, aggregate‐associated C, and soil structure as affected by long‐term land management and slope. A chronosequence of 38 on‐farm sites with low to high (5–18%) slopes was selected to evaluate 5–40 yr of management. The sites were classified as business as usual (BAU) cropland (BAU‐Crop), BAU pasture (BAU‐Past), newly established conservation reserve program (CRP) areas (CRP‐New), and established CRP (CRP‐Old). Soil samples were collected from the 0‐to‐5‐ and 5‐to‐15‐cm depth increments and processed for soil property measurements including fractionation by wet sieving into five aggregate size classes (>2, 000, 1, 000–2, 000, 500–1, 000, 250–500, and 53–250 μm). Within the surface 5 cm, mean weight diameter (MWD) and geometric mean diameter (GMD) were used to characterize soil structural stability. The BAU‐Past and CRP‐Old sites had 79% more macroaggregates (>2, 000, 1, 000–2, 000, and 500–1, 000 μm), 123% higher MWD, 38% higher GMD, and 47% higher SOC than BAU‐Crop or CRP‐New sites. The 5‐to‐15‐cm depth increment showed a similar but lower magnitude response. Aggregate‐associated C was quantified using a constant soil mass that reflected aggregate size distribution to prevent overestimating C content. Lower‐slope locations had more SOC, more macroaggregates, more C associated with macroaggregates, and higher GMD and MWD compared with high‐slope locations across all management classifications and soil depths. The results support our hypothesis that the high‐slop soils may benefits from specific management decisions than the lower‐sloping soils as a function of landscape property. We recommend reestablishing grassland on sloping land that is susceptible to excessive soil erosion, although those practices will likely take a long time to restore soil structural stability and SOC content to precultivation levels. Core Ideas: Land management significantly affected soil structural stability and C dynamics. Cropland was characterized more by microaggregates than macroaggregates. Higher slopes had lower soil structural stability and soil organic C (SOC) than lower slopes. SOC should be measured using a constant mass representing aggregate size distribution. Restoring soil stability to the prairie level will take 10–40 yr or more.